1. Field of the Invention
The present invention relates to a device for determining type of recording media, a method for determining type of recording media, a computer-readable recording medium having recorded therein a program to be executed by a computer for determining type of recording media, and a program to be executed by a computer for determining type of recording media, all of which are appropriately applicable to video game console, DVD device, magneto-optical disc device, and magnetic disc device.
2. Description of the Related Art
There is a conventionally known recording medium with two-dimensional structure where recording layer is “single-layer”, such as CD-ROM or so forth
Further, there is a known recording medium (three-dimensional recording medium) with three-dimensional structure of “multi-layer” where a plurality of recording layers are laminated, such as DVD, FMD (Fluorencent Multi-layer Disc) or so forth, besides the recording medium with two-dimensional structure of “single-layer.”
Device for handling such three-dimensional recording medium must be compatible both for single-layer recording medium having a single recording layer and multi-layer recording medium having two or more recording layers. Such device aimed at handling both of the single-layer and multi-layer recording media should, however, alter settings of laser level or gain of the individual signals between the both.
So that it is a general practice for the device for handling the three-dimensional recording medium to determine whether a recording medium is of single-layer or multi-layer, and alter settings for various portions based on the determined is result to thereby effect recording and reproduction to or from such recording medium.
In a typical case of a DVD device for handling multi-layer DVDs, an optical pick-up makes a gradual approach from a predetermined position towards a DVD so as to generate reproduction signals (sum signals=RF signals), and based on differences in the level of which, whether the disc is of single-layer or multi-layer, or whether the disc is of phase change type such as DVD-RW (level determination method) is determined; or the optical pick-up makes a gradual approach from a predetermined position towards a DVD so as to generate focus error signals (FE signals), and based on count of the number of errors in such FE signal, whether the disc is of single-layer or multi-layer is determined (focus error counting method).
More specifically, in the level determination method, making a gradual approach of an optical pick-up from a predetermined position towards a DVD (for example, making a gradual approach of an optical pick-up from a position distant from a disc (Disc Far) towards a position close thereto (Disc Near)), while keeping the laser level thereof constant, can first generate a reproduction signal (disc surface reflection signal) ascribable to the light reflected on a protective film of the disc typically made from polycarbonate, and can then generate a reproduction signal (signal plane reflection signal) ascribable to the light reflected on a recording layer (signal plane) of the disc.
FIG. 1 shows a disc surface reflection signal and a signal plane reflection signal of a DVD having a single recording layer (referred to as a single-layer DVD, hereinafter). FIG. 2 shows a disc surface reflection signal and a signal plane reflection signal of a DVD having two or more recording layers (referred to as a multi-layer DVD, hereinafter).
As is clear from comparison between FIGS. 1 and 2, there is no difference in the level of disc surface reflection signal between the single-layer (FIG. 1) and multi-layer (FIG. 2) discs on the other hand, the signal plane reflection signal appears as a single peak which is ascribable to the single recording plane for the single-layer DVD and has a larger level P1 , but appears as a peak having a plurality of maximum points corresponded to a plurality of recording planes for the multi-layer DVD (two maximum points corresponded to two recording layers for the case shown in FIG. 2), and having a level P2 lower than that of the single-layer DVD (P1>P2) which is attributable to difference in transmittivity of light of the individual layers, or to random scattering of light by gap between the adjacent layers.
Thus the level determination method conveniently sets a threshold value at an intermittent level between the peak levels obtained for the single-layer DVD and multi-layer DVD, and a DVD is determined as a single-layer one if the level of the signal plane reflection signal thereof is not less than the threshold value, but as a multi-layer DVD or low reflection recording medium (for example, phase-change-type disc) if the level of the signal plane reflection signal thereof is less than the threshold value. This successfully allows determination of recording medium whether it is of single-layer, multi-layer or low reflection type.
On the contrary in the focus error counting method, making a gradual approach of the optical pick-up from a predetermined position towards the DVD, while keeping the laser level thereof constant, gives a focus error signal (FE) as shown in FIG. 3 immediately before and after the focal point on the recording plane for a single-layer DVD, but gives a focus error signal (FE) as shown in FIG. 4 immediately before and after the focal point on the recording plane for a multi-layer DVD.
Thus the focus error counting method conveniently sets a high-level threshold value (FcmpH Slice Level) for such focus error signal, and generates a high-level signal FcmpH during a period that the focus error signal exceeds such high-level threshold value.
Or the system conveniently sets a low-level threshold value (FcmpL Slice Level) for such focus error signal, and generates a FcmpL signal that becomes high-level during a period that the focus error signal becomes lower than such low-level threshold value.
As is clear from comparison of FcmpH signal and FcmpL signal shown in FIG. 3 with those shown in FIG. 4, the single-layer DVD gives only one pulse of the FcmpH signal or FcmpL signal as shown in FIG. 3, and on the contrary the multi-layer DVD gives a plurality of pulses of the FcmpH signal or FcmpL signal as shown in FIG. 4 (for the exemplary case shown in FIG. 4 gives two pulses of the FcmpH signal or FcmpL signal since the DVD has two recording layers).
Thus in the focus error counting method, the disc is determined as a single-layer DVD if the number of pulses is unity, and is determined as a multi-layer DVD if the number of pulses is two or more. This allows determination whether as the DVD has a single or plurality of recording layers
However, the “level determination method” and “focus error counting method”, both or which being conventional determination methods for single-layer disc and multi-layer disc, has suffered from problems below due to their large dependence on signal levels of the reproduction signal and focus error signal.
More specifically, although the “level determination method” is valuable for assessing various gain setting during recording/reproduction, problems of the method reside in that it requires optimum level setting of the threshold values for every instruments for a successful determination of single-layer and multi-layer discs, and in that it only has a narrow allowance for variation in reflectivity of the recording medium due to time-dependent degradation.
On the other hand, the “focus error counting method” suffers from difficulty in setting high-level threshold value (FcmpH Slice Level) or low-level threshold value (FcmpL Slice Level) to an optimum level, which has undesirably resulted in incorrect generation of pulses for the counting, and incorrect counting of the number of pulses due to fake pulse.
The focus error signal (FE) may sometimes have waviness immediately before and after the focal point as shown in FIGS. 3 and 4 depending on mode for detecting focus error, optical design of the optical pick-up, temperature change, signal gain and so forth. The waviness indicated by dotted line in FIGS. 3 and 4 will be causative of fake pulse, which otherwise should not appear, if the level thereof exceeds the high-level threshold value (FcmpH slice Level) or becomes lower than the low-level threshold value (FcmpL Slice Level).
Since the “focus error counting method” makes the single-layer/multi-layer determination by counting the number of pulses of the FcmpH signal or in the FcmpL signal, the fake pulse may give the count value for the FcmpH signal or FcmpL signal different from the true count value thereof, which obstructs correct single-layer/multi-layer determination.
In an exemplary case for the single-layer DVD shown in FIG. 3, the count value may be given as “2”, which should be “1” in true, since also the take pulse indicated by the dotted line is included in the counting, so that the single-layer DVD may be misjudged as a multi-layer DVD